This invention relates to improvements in a brake device for braking an electric motor for an elevator car through brake linings.
Alternating-current (AC) operated elevator systems are constructed such that the induction motor is used to drive an associated elevator car and that, in order that the car is caused to land and stop at any desired floor of a building served by the car, the power supply to the induction motor is interrupted while at the same time a coil of the electromagnetic brake device associated with the motor is denergized to brake a brake wheel directly connected to the induction motor by means of the action of a spring force for the stoppage of the elevator car. However a braking force exerted by the electromagnetic brake device is variable because an associated brake lining for braking the brake wheel by means of a frinctional force developed therebetween has a coefficient of friction changed under the influence of surrounding parameters. Therefore, even with the particular elevator car kept under the same loading, the car can not stop at a predetermined fixed position resulting in a tendency to increase the landing error beyond a predetermined limit.
As a result of repeated experiments conducted with various surrounding parameters affecting the coefficient of friction of the brake lining, it has been confirmed that humidity is one of the surrounding parameters exhibiting the important effects. That is, it has been experimentally discovered that if the brake lining becomes wet that the coefficient of friction thereof increases to stop the associated elevator car somewhat short of a predetermined position assigned to the car even with the same spring force. This has resulted in inaccurate landing of an elevator car.